Airway and lung tissue behaviour during endothelin-1 induced constriction in rats: effects of receptor antagonists.
Endothelin (ET) 1, a 21 amino acid constrictor peptide, is one of the most potent agonists of airway smooth muscle and acts on two different receptors, i.e., ETA and ETB receptors. Recently, it has been shown that there are species and organ differences in physiological roles of each ET receptor. In rats, however, the physiological roles of ET receptors remain to be clarified. We questioned whether ET-1 might affect airway and lung tissue via different ET receptor subtypes in rats. To answer this question, we investigated the effects of ET-1 on lung behaviour in anesthetized, open-chested, mechanically ventilated (f = 1 Hz, VT = 9 mL/kg, PEEP = 3 cmH2O (1 cmH2O = 98.1 Pa)) rats in the absence or the presence of ETA and ETB selective antagonists, i.e., BQ-123 and BQ-788, respectively. Using alveolar capsules, we calculated lung elastance (EL), resistance of lung (RL), tissue (Rti), and airway (Raw), and hysteresivity (eta = 2 pifRti/EL) under control conditions and after intravenous administration of ET-1 (10(-8) mol/kg). ET-1 induced significant increases in RL, Rti, Raw, EL, and eta. BQ-123 did not affect ET-1 induced constriction, while BQ-788 significantly reduced delta RL, delta Rti, delta Raw, delta EL during ET-1 induced constriction. The effects of the combination of BQ-123 and BQ-788 were not different compared with BQ-788. Eta was not affected by BQ-123 and BQ-788. These data suggest that ETB, but not ETA, receptors may have significant physiological roles in rat lungs in response to ET-1.